This invention relates to an operation control system for internal combustion engines, and more particularly to an operation control system of this kind which can control the output of the engine by changing the output in quick response to a change in electrical load on an AC generator driven by the engine.
A control system for controlling an internal combustion engine is known e.g. from Japanese Provisional Patent Publications (Kokai) Nos. 60-150449 and 61-81546, which detects the magnitude of electrical loads applied on the engine from field current flowing in a field winding of an AC generator, calculates a correction value corresponding to the field current, and corrects the valve opening period of a control valve which controls the amount of intake air supplied to the engine, by means of the calculated correction value, to thereby control the output of the engine in response to the magnitude of electrical loads.
The known system is advantageous in being capable of accurately controlling the engine output in response to the magnitude of electrical loads when the electrical loads are in steady state, since the field current exactly represents the magnitude of the electrical loads applied on the engine.
However, the system has the following problem encountered when the electrical loads are in transient state, i.e. when they are changing: In conventional AC generators for automotive engines, usually field current is on-off controlled. Therefore, to detect the field current, the on-off controlled field current is converted into analog current by means of a filter means having a large time constant. More specifically, the field current is on-off controlled by means of a voltage regulator so that the output voltage of the AC generator or that of a battery connected in parallel therewith is maintained constant. A detector for detecting the filed current is provided with a filter means having a large time constant for smoothing the field current to thereby detect same with accuracy. The filter means comprises a hand filter which converts the field current into a ripple-contained voltage, and a soft filter which smooths or averages the ripple-contained voltage when the electrical loads are in steady state.
However, the use of the filter means for detecting the field current actually involves a time delay in the detection of a change in the magnitude of electrical loads.
That is, since the field current is detected with a time lag corresponding to the time constant of the filter means, the correction of the intake air amount which is started upon the detection of a change in the field current is too late for the engine output to be changed in accordance with the change in the field current or in the magnitude of electrical loads. This control delay can cause a drop in the rotational speed of the engine, for example. Thus, in the conventional engine operation control system, the engine output control is difficult to carry out with high accuracy and high responsiveness to a transient state of the electrical loads on the engine.